tahoe-lafs/docs/webapi.txt

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This document has six sections:
1. the basic API for how to programmatically control your tahoe node
2. convenience methods
3. safety and security issues
4. features for controlling your tahoe node from a standard web browser
5. debugging and testing features
6. XML-RPC (coming soon)
1. the basic API for how to programmatically control your tahoe node
a. connecting to the tahoe node
Writing "8123" into $NODEDIR/webport causes the node to run a webserver on
port 8123. Writing "tcp:8123:interface=127.0.0.1" into $NODEDIR/webport does
the same but binds to the loopback interface, ensuring that only the programs
on the local host can connect. Using
"ssl:8123:privateKey=mykey.pem:certKey=cert.pem" would run an SSL server. See
twisted.application.strports for more details.
This webport can be set when the node is created by passing a --webport
option to the 'tahoe create-client' command. By default, the node listens on
port 8123, on the loopback (127.0.0.1) interface.
b. file names
The node provides some small number of "virtual drives". In the 0.5 release,
this number is two: the first is the global shared vdrive, the second is the
private non-shared vdrive. We will call the global one "global", and we will
refer to the second one by "$PRIVATE_VDRIVE_URI", to show that to use it you
have to insert the specific URI for that private vdrive.
For the purpose of this document, let us assume that the vdrives currently
contain the following directories and files:
global/
global/Documents/
global/Documents/notes.txt
$PRIVATE_VDRIVE_URI/
$PRIVATE_VDRIVE_URI/Pictures/
$PRIVATE_VDRIVE_URI/Pictures/tractors.jpg
$PRIVATE_VDRIVE_URI/Pictures/family/
$PRIVATE_VDRIVE_URI/Pictures/family/bobby.jpg
Within the webserver, there is a tree of resources. The top-level "vdrive"
resource gives access to files and directories in all of the user's virtual
drives. For example, the URL that corresponds to notes.txt would be:
http://localhost:8123/vdrive/global/Documents/notes.txt
and the URL for tractors.jpg would be:
http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/Pictures/tractors.jpg
In addition, each directory has a corresponding URL. The Pictures URL is:
http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/Pictures
c. URIs
From the "URIs" chapter in architecture.txt, recall that each file and
directory has a unique "URI". This is a string which provides a secure
reference to the file or directory: if you know the URI, you can retrieve
(and possibly modify) the object. If you don't know the URI, you cannot
access the object.
A separate top-level namespace ("uri/" instead of "vdrive/") is used to
access to files and directories directly by URI, rather than by going through
the pathnames in the vdrive.
For example, this identifies a file or directory:
http://localhost:8123/uri/$URI
And this identifies a file or directory named "tractors.jpg" in a
subdirectory "Pictures" of the identified directory:
http://localhost:8123/uri/$URI/Pictures/tractors.jpg
In the following examples, "$URL" is a shorthand for a URL like the ones
above, either with "vdrive/" and a vdrive name as the top level and a
sequence of slash-separated pathnames following, or with "uri/" as the top
level, followed by a URI, optionally followed by a sequence of
slash-separated pathnames.
Note that since tahoe URIs may contain slashes (in particular, dirnode URIs
contain a FURL, which resembles a regular HTTP URL and starts with pb://),
when URIs are used in this form, they must be specially quoted. All slashes
in the URI must be replaced by '!' characters. The intent is to remove this
unpleasant requirement in a future release: please see ticket #102 for
details. An example of this sort of directory-URI URL is:
http://localhost:8123/uri/URI%3ADIR%3Apb%3A!!xextf3eap44o3wi27mf7ehiur6wvhzr6%40207.7.153.180%3A56677%2C127.0.0.1%3A56677!vdrive%3Agqu1fub33exw9cu63718yzx6gr/
Now, what can we do with these URLs? By varying the HTTP method
(GET/PUT/POST/DELETE) and by appending a type-indicating query argument, we
control what we want to do with the data and how it should be presented.
d. examining files or directories
GET $URL?t=json
This returns machine-parseable information about the indicated file or
directory in the HTTP response body. The JSON always contains a list, and
the first element of the list is always a flag that indicates whether the
referenced object is a file or a directory.
If it is a file, then the information includes file size and URI, like
this:
[ 'filenode', { 'ro_uri': file_uri,
'size': bytes } ]
If it is a directory, then it includes information about the children of
this directory, as a mapping from child name to a set of metadata about the
child (the same data that would appear in a corresponding GET?t=json of the
child itself). Like this:
[ 'dirnode', { 'rw_uri': read_write_uri,
'ro_uri': read_only_uri,
'children': children } ]
In the above example, 'children' is a dictionary in which the keys are
child names and the values depend upon whether the child is a file or a
directory:
'foo.txt': [ 'filenode', { 'ro_uri': uri, 'size': bytes } ]
'subdir': [ 'dirnode', { 'rw_uri': rwuri, 'ro_uri': rouri } ]
note that the value is the same as the JSON representation of the child
object (except that directories do not recurse -- the "children" entry of
the child is omitted).
Then the rw_uri field will be present in the information about a directory
if and only if you have read-write access to that directory,
e. downloading a file
GET $URL
If the indicated object is a file, then this simply retrieves the contents
of the file. The file's contents are provided in the body of the HTTP
response.
If the indicated object a directory, then this returns an HTML page,
intended to be displayed to a human by a web browser, which contains HREF
links to all files and directories reachable from this directory. These
HREF links do not have a t= argument, meaning that a human who follows them
will get pages also meant for a human. It also contains forms to upload new
files, and to delete files and directories. These forms use POST methods to
do their job.
You can add the "save=true" argument, which adds a 'Content-Disposition:
attachment' header to prompt most web browsers to save the file to disk
rather than attempting to display it.
A filename (from which a MIME type can be derived, for use in the
Content-Type header) can be specified using a 'filename=' query argument.
This is especially useful if the $URL does not end with the name of the
file (e.g. if it ends with the URI of the file instead). This filename is
also the one used if the 'save=true' argument is set. For example:
GET http://localhost:8123/uri/$TRACTORS_URI?filename=tractors.jpg
f. uploading a file
PUT http://localhost:8123/uri
Upload a file, returning its URI as the HTTP response body. This does not
make the file visible from the virtual drive -- to do that, see section
1.h. below, or the convenience method in section 2.a..
g. creating a new directory
PUT http://localhost:8123/uri?t=mkdir
Create a new empty directory and return its URI as the HTTP response body.
This does not make the newly created directory visible from the virtual
drive, but you can use section 1.h. to attach it, or the convenience method
in section 2.XXX.
h. attaching a file or directory as the child of an extant directory
PUT $URL?t=uri
This attaches a child (either a file or a directory) to the given directory
$URL is required to indicate a directory as the second-to-last element and
the desired filename as the last element, for example:
PUT http://localhost:8123/uri/$URI_OF_SOME_DIR/Pictures/tractors.jpg
PUT http://localhost:8123/uri/$URI_OF_SOME_DIR/tractors.jpg
PUT http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/Pictures/tractors.jpg
(Note that a URI_OF_SOME_DIR and a PRIVATE_VDRIVE_URI are each just
separate URIs, and there is nothing special about the latter except that it
is useful to put all of the user's top-level files and directories into one
place, so we choose to use that particular directory to be the user's main
directory.)
The URI of the child is provided in the body of the HTTP request.
There is an optional "?replace=" param whose value can be "true", "t", "1",
"false", "f", or "0" (case-insensitive), and which defaults to "true". If
the indicated directory already contains the given child name, then if
replace is true then the value of that name is changed to be the new URI.
If replace is false then an HTTP 409 "Conflict" error is returned.
This can be used to attach a shared directory (a directory that other
people can read or write) to the vdrive. Intermediate directories, if any,
are created on-demand.
i. removing a name from a directory
DELETE $URL
This removes the given name from the given directory. $URL is required to
indicate a directory as the second-to-last element and the name to remove
from that directory as the last element, just as in section 1.g..
Note that this does not actually delete the resource that the name points
to from the tahoe grid -- it only removes this name in this directory. If
there are other names in this directory or in other directories that point
to the resource, then it will remain accessible through those paths. Even
if all names pointing to this resource are removed from their parent
directories, then if someone is in possession of the URI of this resource
they can continue to access the resource through the URI. Only if a person
is not in possession of the URI, and they do not have access to any
directories which contain names pointing to this resource, are they
prevented from accessing the resource. (This behavior is very similar to
the way hardlinks and anonymous files work in traditional unix
filesystems).
2. convenience methods
a. uploading a file and attaching it to the vdrive
PUT $URI
Upload a file and link it into the the vdrive at the location specified by
$URI. The last item in the $URI must be a filename, and the second-to-last
item must identify a directory.
It will create intermediate directories as necessary. The file's contents
are taken from the body of the HTTP request. For convenience, the HTTP
response contains the URI that results from uploading the file, although
the client is not obligated to do anything with the URI. According to the
HTTP/1.1 specification (rfc2616), this should return a 200 (OK) code when
modifying an existing file, and a 201 (Created) code when creating a new
file. (TODO: as of 0.5, the web server only returns 200, never 201).
To use this, run 'curl -T localfile http://localhost:8123/vdrive/global/newfile'
3. safety and security issues -- names vs. URIs
The vdrive provides a mutable filesystem, but the ways that the filesystem
can change are limited. The only thing that can change is that the mapping
from child names to child objects that each directory contains can be changed
by adding a new child name pointing to an object, removing an existing child
name, or changing an existing child name to point to a different object.
Obviously if you query tahoe for information about the filesystem and then
act upon the filesystem (such as by getting a listing of the contents of a
directory and then adding a file to the directory), then the filesystem might
have been changed after you queried it and before you acted upon it.
However, if you use the URI instead of the pathname of an object when you act
upon the object, then the only change that can happen is when the object is a
directory then the set of child names it has might be different. If, on the
other hand, you act upon the object using its pathname, then a different
object might be in that place, which can result in more kinds of surprises.
For example, suppose you are writing code which recursively downloads the
contents of a directory. The first thing your code does is fetch the listing
of the contents of the directory. For each child that it fetched, if that
child is a file then it downloads the file, and if that child is a directory
then it recurses into that directory. Now, if the download and the recurse
actions are performed using the child's name, then the results might be
wrong, because for example a child name that pointed to a sub-directory when
you listed the directory might have been changed to point to a file (in which
case your attempt to recurse into it would result in an error and the file
would be skipped), or a child name that pointed to a file when you listed the
directory might now point to a sub-directory (in which case your attempt to
download the child would result in a file containing HTML text describing the
sub-directory!).
If your recursive algorithm uses the uri of the child instead of the name of
the child, then those kinds of mistakes just can't happen. Note that both the
child's name and the child's URI are included in the results of listing the
parent directory, so it isn't any harder to use the URI for this purpose.
In general, use names if you want "whatever object (whether file or
directory) is found by following this name (or sequence of names) when my
request reaches the server". Use URIs if you want "this particular object".
4. features for controlling your tahoe node from a standard web browser
a. uri redirect
GET http://localhost:8123/uri?uri=$URI
This causes a redirect to /uri/$URI, and retains any additional query
arguments (like filename= or save=). This is for the convenience of web
forms which allow the user to paste in a URI (obtained through some
out-of-band channel, like IM or email).
Note that this form merely redirects to the specific file or directory
indicated by the URI: unlike the GET /uri/$URI form, you cannot traverse to
children by appending additional path segments to the URL.
b. web page offering rename
GET $URL?t=rename-form&name=$CHILDNAME
This provides a useful facility to browser-based user interfaces. It
returns a page containing a form targetting the "POST $URL t=rename"
functionality described below, with the provided $CHILDNAME present in the
'from_name' field of that form. I.e. this presents a form offering to
rename $CHILDNAME, requesting the new name, and submitting POST rename.
c. POST forms
POST $URL
t=upload
name=childname (optional)
file=newfile
This instructs the node to upload a file into the given directory. We need
this because forms are the only way for a web browser to upload a file
(browsers do not know how to do PUT or DELETE). The file's contents and the
new child name will be included in the form's arguments. This can only be
used to upload a single file at a time. To avoid confusion, name= is not
allowed to contain a slash (a 400 Bad Request error will result).
POST $URL
t=upload
name=childname (optional)
mutable="on"
file=newfile
This instructs the node to upload a file into the given directory, using a
mutable file (SSK) rather than the usual immutable file (CHK).
POST $URL
t=mkdir
name=childname
This instructs the node to create a new empty directory. The name of the
new child directory will be included in the form's arguments.
POST $URL
t=uri
name=childname
uri=newuri
This instructs the node to attach a child that is referenced by URI (just
like the PUT $URL?t=uri method). The name and URI of the new child
will be included in the form's arguments.
POST $URL
t=delete
name=childname
This instructs the node to delete a file from the given directory. The name
of the child to be deleted will be included in the form's arguments.
POST $URL
t=rename
from_name=oldchildname
to_name=newchildname
This instructs the node to rename a child within the given directory. The
child specified by 'from_name' is removed, and reattached as a child named
for 'to_name'. This is unconditional and will replace any child already
present under 'to_name', akin to 'mv -f' in unix parlance.
5. debugging and testing features
GET $URL?t=download&localfile=$LOCALPATH
GET $URL?t=download&localdir=$LOCALPATH
The localfile= form instructs the node to download the given file and write
it into the local filesystem at $LOCALPATH. The localdir= form instructs
the node to recursively download everything from the given directory and
below into the local filesystem. To avoid surprises, the localfile= form
will signal an error if $URL actually refers to a directory, likewise if
localdir= is used with a $URL that refers to a file.
This request will only be accepted from an HTTP client connection
originating at 127.0.0.1 . This request is most useful when the client node
and the HTTP client are operated by the same user. $LOCALPATH should be an
absolute pathname.
This form is only implemented for testing purposes, because of a trivially
easy attack: any web server that the local browser visits could serve an
IMG tag that causes the local node to modify the local filesystem.
Therefore this form is only enabled if you create a file named
'webport_allow_localfile' in the node's base directory.
PUT $NEWURL?t=upload&localfile=$LOCALPATH
PUT $NEWURL?t=upload&localdir=$LOCALPATH
This uploads a file or directory from the node's local filesystem to the
vdrive. As with "GET $URL?t=download&localfile=$LOCALPATH", this request
will only be accepted from an HTTP connection originating from 127.0.0.1 .
The localfile= form expects that $LOCALPATH will point to a file on the
node's local filesystem, and causes the node to upload that one file into
the vdrive at the given location. Any parent directories will be created in
the vdrive as necessary.
The localdir= form expects that $LOCALPATH will point to a directory on the
node's local filesystem, and it causes the node to perform a recursive
upload of the directory into the vdrive at the given location, creating
parent directories as necessary. When the operation is complete, the
directory referenced by $NEWURL will contain all of the files and
directories that were present in $LOCALPATH, so this is equivalent to the
unix commands:
mkdir -p $NEWURL; cp -r $LOCALPATH/* $NEWURL/
Note that the "curl" utility can be used to provoke this sort of recursive
upload, since the -T option will make it use an HTTP 'PUT':
curl -T /dev/null 'http://localhost:8123/vdrive/global/newdir?t=upload&localdir=/home/user/directory-to-upload'
This form is only implemented for testing purposes, because any attacker's
web server that a local browser visits could serve an IMG tag that causes
the local node to modify the local filesystem. Therefore this form is only
enabled if you create a file named 'webport_allow_localfile' in the node's
base directory.
GET $URL?t=manifest
Return an HTML-formatted manifest of the given directory, for debugging.
6. XMLRPC (coming soon)
http://localhost:8123/xmlrpc
This resource provides an XMLRPC server on which all of the previous
operations can be expressed as function calls taking a "pathname" argument.
This is provided for applications that want to think of everything in terms
of XMLRPC.
listdir(vdrivename, path) -> dict of (childname -> (stuff))
put(vdrivename, path, contents) -> URI
get(vdrivename, path) -> contents
mkdir(vdrivename, path) -> URI
put_localfile(vdrivename, path, localfilename) -> URI
get_localfile(vdrivename, path, localfilename)
put_localdir(vdrivename, path, localdirname) # recursive
get_localdir(vdrivename, path, localdirname) # recursive
put_uri(vdrivename, path, URI)
etc..